1. Filed of the Invention
This invention relates to an ophthalmologic apparatus, and more particularly to an ophthalmologic apparatus comprising an illumination optical system for directing illumination light onto a prescribed point of an eye under examination and an observation optical system for observing an image of the prescribed point of the eye under examination formed through an object lens.
2. Description of the Prior Art
In conventional apparatuses used in ophthalmological treatment such as the slit lamp microscope, white light from a light source, such as a halogen lamp is passed through a slit formed between the opposing edges of two shield plates. The slit beam obtained in this way is directed onto a prescribed point on the cornea, crystalline lens or the like of the eye under examination. The scattered light from the illuminated point passes through an object lens of an observation optical system and the resulting image of the point can be observed for examining the condition of the cornea, crystalline lens etc.
One method used for varying the magnification factor in order to enlarge or reduce the observed image has been to insert or remove a lens into or from the observation optical system. However, this method requires a mechanism for insertion and removal of lenses and thus increases the complexity of the overall structure of the apparatus. Other methods that have been used for this purpose include one in which magnification of the observed image is varied by loading lenses into a turret and then rotating the turret to bring a lens of the required power into the light path. In another method the magnification is varied by moving a zoom lens built into the observation optical system along the optical axis. With either of these arrangements, however, the number of lenses is increased and it becomes necessary to control the lens intervals and decentering, which increases the complexity of the apparatus and increases its weight.